1. Field of the Invention
The present invention relates to an image forming apparatus such as an electrophotographic copier, laser printer or facsimile machine.
2. Description of the Related Art
An electrophotographic method using toner is often used for the image forming apparatus such as an electrophotographic copier, laser printer or facsimile machine. The electrophotographic method includes a transfer step of electrostatically transferring toner images, i.e., developed images, carried on a photosensitive drum which acts as an image bearing member to a surface of a transfer material or intermediate transfer belt.
Japanese Patent Application Laid-Open No. 2009-204809 discloses a configuration in which a transfer member is placed across a transfer material conveyance belt or intermediate transfer belt from a photosensitive drum (i.e., placed on the back side of the transfer material conveyance belt or intermediate transfer belt) by being fixed to a support member such as a transfer sheet and put in contact with the belt without rotating with respect to the support member. The belt and the transfer member can form a relatively large contact surface area, resulting in improved transferability. However, the transfer member, which is fixed to the support member and placed in contact with the belt without rotating with respect to the support member, has the following problem.
Foreign material such as dust may sometimes get inside the belt. When such dust enters between the inner face of the belt and the transfer member, condition of contact between the belt and the transfer member becomes non-uniform in a longitudinal direction of the belt orthogonal to the movement direction of the belt. When the condition of contact becomes non-uniform in the longitudinal direction of the belt, a phenomenon of density irregularities will occur when a toner image is transferred from the image bearing member. The phenomenon of density irregularities involves vertical streaks in the belt movement direction or bands of shading. This is considered to be because the dust trapped between the inner face of the belt and the transfer member causes an unstable state of discharge in the longitudinal direction or differences in longitudinal pressure distribution to thereby cause irregular abrasion on the image bearing member.